Methods of forming silicon dioxide layers and methods of forming trench isolation regions

ABSTRACT

In one aspect, the invention includes a method of forming a silicon dioxide layer, including: a) forming a high density plasma proximate a substrate, the plasma including silicon dioxide precursors; b) forming silicon dioxide from the precursors, the silicon dioxide being deposited over the substrate at a deposition rate; and c) while depositing, etching the deposited silicon dioxide with the plasma at an etch rate; a ratio of the deposition rate to the etch rate being at least about 4:1. In another aspect, the invention includes a method of forming a silicon dioxide layer, including: a) forming a high density plasma proximate a substrate; b) flowing gases into the plasma, at least some of the gases forming silicon dioxide; c) depositing the silicon dioxide formed from the gases over the substrate; and d) while depositing the silicon dioxide, maintaining a temperature of the substrate at greater than or equal to about 500° C. In yet another aspect, the invention includes a method of forming a silicon dioxide layer, including: a) forming a high density plasma proximate a substrate; b) flowing gases into the plasma, at least some of the gases forming silicon dioxide; c) depositing the silicon dioxide formed from the gases over the substrate; and d) not cooling the substrate with a coolant gas while depositing the silicon dioxide.

This is a divisional of application of Ser. No. 09/554,754, filed May19, 2000, the entirre disclosure of which is hereby incorporated byreference.

TECHNICAL FIELD

The invention pertains to methods of forming silicon dioxide layers,such as, for example, methods of forming trench isolation regions.

BACKGROUND OF THE INVENTION

Integrated circuitry is typically fabricated on and within semiconductorsubstrates, such as bulk monocrystalline silicon wafers. In the contextof this document, the term “semiconductive substrate” is defined to meanany construction comprising semiconductive material, including, but notlimited to, bulk semiconductive materials such as a semiconductive wafer(either alone or in assemblies comprising other materials thereon), andsemiconductive material layers (either alone or in assemblies comprisingother materials). The term “substrate” refers to any supportingstructure including, but not limited to, the semiconductive substratesdescribed above.

Electrical components fabricated on substrates, and particularly bulksemiconductor wafers, are isolated from adjacent devices by insulatingmaterials, such as silicon dioxide. One isolation technique uses shallowtrench isolation, whereby trenches are cut into a substrate and aresubsequently filled with an insulating material, such as, for example,silicon dioxide. In the context of this document, “shallow” shall referto a distance of no greater than about 1 micron from an outermostsurface of a substrate material within which an isolation region isreceived.

A prior art method for forming a trench isolation region, such as ashallow trench isolation region, is described with reference to FIGS.1-2. FIG. 1 illustrates a semiconductor wafer fragment 10 at apreliminary step of the prior art processing method. Wafer fragment 10comprises a substrate 12, a pad oxide layer 14 over substrate 12, and asilicon nitride layer 16 over pad oxide layer 14. Substrate 12 cancomprise, for example, a monocrystalline silicon wafer lightly dopedwith a p-type background dopant. Pad oxide layer 14 can comprise, forexample, silicon dioxide.

Openings 22 extend through layers 14 and 16, and into substrate 12.Openings 22 can be formed by, for example, forming a patterned layer ofphotoresist over layers 14 and 16 to expose regions where openings 22are to be formed and to cover other regions. The exposed regions canthen be removed to form openings 22, and subsequently the photoresistcan be stripped from over layers 14 and 16.

A first silicon dioxide layer 24 is formed within openings 22 to athickness of, for example, about 100 Angstroms. First silicon dioxidelayer 24 can be formed by, for example, heating substrate 12 in thepresence of oxygen. A second silicon dioxide layer 26 is depositedwithin the openings by high density plasma deposition. In the context ofthis document, a high density plasma is a plasma having a density ofgreater than or equal to about 10¹⁰ ions/cm³.

FIG. 1 is a view of wafer fragment 10 as opening 22 is partially filledwith the deposited silicon dioxide, and FIG. 2 is a view of the waferfragment after the openings have been completely filled. As shown inFIG. 1, the deposited silicon dioxide undesirably forms cusps 28 at topportions of openings 22. Specifically, cusps 28 are formed over cornersof silicon nitride layer 16 corresponding to steps in elevation. Thecusp formation (also referred to as “bread-loafing”) interferes withsubsequent deposition of silicon dioxide layer 26 as shown in FIG. 2.Specifically, the subsequently deposited silicon dioxide can fail tocompletely fill openings 22, resulting in the formation of voids 29, or“keyholes” within the deposited silicon dioxide layer 26.

After providing second silicon dioxide layer 26 within openings 22, thesecond silicon dioxide layer is planarized, preferably to a levelslightly below an upper surface of nitride layer 16, to form silicondioxide plugs within openings. The silicon dioxide plugs define trenchisolation regions within substrate 12. Such trench isolation regionshave voids 29 remaining within them. The voids define a space within thetrench isolation regions having a different dielectric constant than theremainder of the trench isolation regions, and can undesirably allowcurrent leakage through the trench isolation regions. Accordingly, it isdesirable to develop methods of forming trench isolation regions whereinvoids 29 are avoided.

SUMMARY OF THE INVENTION

In one aspect, the invention encompasses a method of forming a silicondioxide layer. A high density plasma is formed proximate a substrate.The plasma comprises silicon dioxide precursors. Silicon dioxide isformed from the precursors and deposited over the substrate at adeposition rate. While the silicon dioxide is being deposited, it isetched with the plasma at an etch rate. A ratio of the deposition rateto the etch rate is at least about 4:1.

In another aspect, the invention encompasses a method of forming asilicon dioxide layer over a substrate wherein a temperature of thesubstrate is maintained at greater than or equal to about 500° C. duringthe deposition. More specifically, a high density plasma is formedproximate a substrate. Gases are flowed into the plasma, and at leastsome of the gases form silicon dioxide. The silicon dioxide is depositedover the substrate. While the silicon dioxide is being deposited, atemperature of the substrate is maintained at greater than or equal toabout 500° C.

In another aspect, the invention encompasses a method of forming asilicon dioxide layer over a substrate wherein the substrate is notcooled during the deposition. More specifically, a high density plasmais formed proximate a substrate. Gases are flowed into the plasma, andat least some of the gases form silicon dioxide. The silicon dioxide isdeposited over the substrate. The substrate is not cooled with a coolantgas while depositing the silicon dioxide.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a fragmentary, diagrammatic, cross-sectional view of asemiconductor wafer fragment at a preliminary step of a prior artfabrication process.

FIG. 2 is a view of the FIG. 1 wafer fragment shown at a prior artprocessing step subsequent to that of FIG. 1.

FIG. 3 is a diagrammatic, cross-sectional view of a reaction chamberconfigured for utilization in a method of the present invention.

FIG. 4 is a diagrammatic cross-sectional view of a semiconductor waferfragment processed in accordance with the present invention. The waferfragment of FIG. 4 is shown at a processing step similar to the priorart processing step shown in FIG. 1.

FIG. 5 is a view of the FIG. 4 wafer fragment shown at a processing stepsubsequent to that of FIG. 4.

FIG. 6 is a view of the FIG. 4 wafer fragment shown at a processing stepsubsequent to that of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

The present invention encompasses methods of increasing a deposition toetch ratio in a high density plasma reaction chamber during formation ofa silicon dioxide layer. A high density plasma reaction chamber 40 isillustrated in FIG. 3. Reaction chamber 40 comprises a vessel 42surrounded by inductive coils 44. Inductive coils 44 are connected to afirst power source 46 which can be configured to provide power, such as,for example, RF energy, within coils 44. Reaction chamber 40 furthercomprises a chuck 48 configured for holding a semiconductive wafer 45within vessel 42. Wafer 45 is connected through chuck 48 to a powersource 50 which can be configured to, for example, produce RF energywithin wafer 45.

In operation, plasma precursor gasses (not shown) are flowed into vessel42. Power source 46 is utilized to provide a first bias, of, forexample, a power of from about 1000 watts to about 8000 watts toinductive coils 44, which generates a plasma 56 within vessel 42. Secondpower source 50 is utilized to provide a second bias, of, for example, apower of from about 1000 watts to about 5000 watts to wafer 45.

Among the plasma precursor gasses are silicon dioxide precursors suchas, for example, SiH₄ and oxygen, as well as other plasma components,such as, for example, Ar. Plasma 56 can, for example, be formed from agas consisting essentially of SiH₄, O₂ and Ar. The silicon dioxideprecursors form silicon dioxide which is deposited on wafer 45 at adeposition rate. Also, during the depositing, the silicon dioxide isetched at an etch rate.

In prior art processes, the chuck is cooled to maintain the wafer at atemperature of less than or equal to 300° C. In contrast, in a processof the present invention, chuck 48 is not cooled. Accordingly, wafer 10is permitted to heat within vessel 42 during a present inventiondeposition process by energy transferred from plasma 56. Preferably,wafer 45 is maintained at temperatures of at least about 500° C., butpreferably is removed before its temperature exceeds about 1000° C.

It is observed that a significant etch of the deposited material occursprimarily when wafer 45 is biased within vessel 42. Accordingly, amethod for measuring the deposition rate is to remove any bias powerfrom wafer 45, and to keep other reaction parameters appropriate fordeposition of silicon dioxide. Silicon dioxide will then be deposited onwafer 45 without etching.

To determine an etch rate occurring within chamber 42 during adeposition process, a wafer 45 having an exposed layer of silicondioxide is provided within the reaction chamber. The reaction parameterswithin the chamber are then adjusted as they would be for a depositionprocess, with the wafer being biased as would occur in a typicaldeposition process, but there being no feed of silicon dioxideprecursors to the chamber. Accordingly, etching of the silicon dioxidelayer occurs without additional growth of silicon dioxide.

Measurements conducted relative to a prior art high density plasmadeposition process reveal that a ratio of the deposition rate to theetch rate is less than about 3.4:1 for trenches having an aspect ratioof from about 2.5 to about 1. In contrast measurements conductedrelative to a high density plasma deposition process of the presentinvention reveal that by maintaining wafer 45 at temperatures of atleast about 500° C., the ratio of the deposition rate to the etch ratecan be increased to at least about 4:1, more preferably to at leastabout 6:1, and still more preferably to at least about 9:1. The ratio ofdeposition rate to etch rate varies with an aspect ratio of a trenchbeing filled.

It is observed that the void formation described above with reference toFIG. 1 can be reduced, or even eliminated, by increasing adeposition-to-etch ratio of a high density plasma deposition process.

Referring to FIGS. 4-6, a deposition process of the present invention isillustrated. In describing FIGS. 4-6, similar numbering to that utilizedabove in describing the prior art FIGS. 1 and 2 will be used, withdifferences indicated by the suffix “a” or by different numerals. FIG. 4illustrates a semiconductor wafer fragment 10 a shown at a processingstep corresponding to that of the prior art wafer fragment 10 of FIG. 1.Wafer fragment 10 a can, for example, be a portion of the wafer 45 aillustrated in FIG. 3. Wafer fragment 10 a comprises a layer of silicondioxide 26 a deposited over a substrate 12 a and within openings 22 a. Adifference between wafer fragment 10 a of FIG. 4, and wafer fragment 10of FIG. 1, is that the high deposition-toetch ratio of the presentinvention has significantly eliminated cusps 28 (FIG. 1). In otherwords, the high deposition-to-etch ratio of the present invention hasachieved a more conformal coating of silicon dioxide layer 26 a over theelevational step of an upper corner of nitride layer 16 than could beachieved with prior art processing methods. Such more conformal coatingcan be referred to as “better step coverage”.

Referring to FIG. 5, wafer fragment 10 a is illustrated after silicondioxide deposition has progressed to fill openings 22 a with silicondioxide layer 26 a. Wafer fragment 10 a of FIG. 5 is illustrated at aprocessing step analogous to the prior art step illustrated in FIG. 2. Adifference between wafer fragment 10 a of FIG. 5 and prior art waferfragment 10 of FIG. 2 is that keyholes 29 are eliminated from fragment10 a.

Referring to FIG. 6, wafer fragment 10 a is illustrated afterplanarizing silicon dioxide layer 26 a (FIG. 5) and removing siliconnitride layer 16 to form shallow trench isolation regions 32. Shallowtrench isolation regions 32 comprise the planarized second silicondioxide layer and thermally grown silicon dioxide 24 a. Trench isolationregions 32 lack the voids 29 that had been problematic in prior arttrench isolation regions.

It is noted that the process of the present invention is described withreference to the reaction chamber construction of FIG. 3 for purposes ofillustration only. The present invention can, of course, be utilizedwith other reaction chamber constructions, such as, for example,transformer coupled plasma reactors.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

What is claimed is:
 1. A method of forming a silicon dioxide layer,comprising: forming a high density plasma proximate a substrate; flowinggases into the plasma, at least some of the gases forming silicondioxide; depositing the silicon dioxide formed from the gases over thesubstrate; and while depositing the silicon dioxide, maintaining atemperature of the substrate at greater than 700° C. to about 1000° C.2. The method of claim 1 further comprising: forming openings in thesubstrate; and depositing the silicon dioxide within the openings. 3.The method of claim 1 wherein the gases comprise SiH₄ and oxygen.
 4. Themethod of claim 1 wherein the gases comprise SiH₄, oxygen and argon. 5.A method of forming a silicon dioxide layer, comprising: forming a highdensity plasma proximate a substrate; flowing gases into the plasma, atleast some of the gases forming silicon dioxide; depositing the silicondioxide formed from the gases over the substrate without cooling thesubstrate with a coolant gas while depositing the silicon dioxide. 6.The method of claim 5 further comprising maintaining a temperature ofthe substrate at greater than or equal to 500° C. during the depositing.7. A method of forming a silicon dioxide layer, comprising: forming ahigh density plasma proximate a substrate; flowing gases into theplasma, at least some of the gases forming silicon dioxide; depositingthe silicon dioxide formed from the gases over the substrate at adeposition rate; while depositing, etching the deposited silicon dioxidewith the plasma at an etch rate; and during the etching and depositing,maintaining a temperature of the substrate at greater than 700° C. toabout 1000° C.
 8. The method of claim 7 wherein the gases comprise SiH₄and oxygen.
 9. The method of claim 7 wherein the gases comprise SiH₄,oxygen and argon.
 10. The method of claim 7 further comprising: formingopenings in the substrate; and depositing the silicon dioxide within theopenings.
 11. A method of forming a silicon dioxide layer, comprising:forming a high density plasma proximate a substrate; flowing gases intothe plasma, at least some of the gases forming silicon dioxide;depositing the silicon dioxide formed from the gases over the substrateat a deposition rate; while depositing, etching the deposited silicondioxide with the plasma at an etch rate; and during the etching anddepositing, maintaining a temperature of the substrate at greater thanor equal to about 500° C., the maintaining a temperature comprising notexposing the substrate to a coolant gas.
 12. A method of forming asilicon dioxide layer, comprising: forming a high density plasmaproximate a substrate; flowing gases into the plasma, at least some ofthe gases forming silicon dioxide; depositing the silicon dioxide formedfrom the gases over the substrate at a deposition rate; and whiledepositing, etching the deposited silicon dioxide with the plasma at anetch rate under elevated temperature conditions to achieve a ratio ofdeposition rate to etch rate of at least about 6:1 throughout theetching and depositing until completing formation of the silicon dioxidelayer, the ratio being at least two-times greater than another ratiounder identical processing conditions of an identical substrate exceptat lower temperature conditions less than or equal to 300° C.
 13. Amethod of forming a silicon dioxide layer, comprising: forming a highdensity plasma proximate a substrate, the plasma comprising silicondioxide precursors, the substrate comprising an opening having an aspectratio of at least about 1; forming silicon dioxide from the precursors,the silicon dioxide being deposited within the opening at a depositionrate; and while depositing, etching the silicon dioxide deposited withinthe opening, the etching comprising etching with the plasma at an etchrate; a ratio of the deposition rate to the etch rate being at leastabout 6:1 throughout the etching and depositing until completingformation of the silicon dioxide layer.
 14. The method of claim 13wherein the opening has an aspect ratio of from about 2.5 to about 1.15. The method of claim 13 further comprising: placing the substrate ina reaction chamber, the reaction chamber comprising inductive coils togenerate the plasma; the depositing and etching occurring in thereaction chamber; providing a first bias to the inductive coils; andduring the etching, providing a second bias to the substrate.
 16. Amethod of forming a silicon dioxide layer, comprising: forming a highdensity plasma proximate a substrate, the substrate comprising anopening having an aspect ratio of at least about 1; flowing gases intothe plasma, at least some of the gases forming silicon dioxide;depositing the silicon dioxide formed from the gases within the openingat a deposition rate; and while depositing, etching the silicon dioxidedeposited within the opening with the plasma at an etch rate; a ratio ofthe deposition rate to the etch rate being at least about 6:1 throughoutthe etching and depositing until completing formation of the silicondioxide layer.
 17. The method of claim 16 wherein the opening has anaspect ratio of from about 2.5 to about
 1. 18. The method of claim 16further comprising maintaining a temperature of the substrate at greaterthan 700° C. to about 1000° C.
 19. The method of claim 16 wherein theratio of the deposition rate to the etch rate is at least about 9:1. 20.The method of claim 16 further comprising maintaining a temperature ofthe substrate at greater than or equal to about 500° C. during thedeposition and etching.
 21. The method of claim 16 further comprising:forming openings in the substrate; and depositing the silicon dioxidewithin the openings.
 22. The method of claim 16 wherein the gasescomprise SiH₄ and oxygen.
 23. The method of claim 16 wherein the gasescomprise SiH₄, oxygen and argon.
 24. The method of claim 16 wherein thegases are a mixture consisting essentially of SiH₄, oxygen and argon.25. A method of forming a silicon dioxide layer, comprising: forming ahigh density plasma proximate a substrate, the substrate comprising astep; flowing gases into the plasma, at least some of the gases formingsilicon dioxide; depositing the silicon dioxide formed from the gasesover the substrate step; and while depositing the silicon dioxide,maintaining a temperature of the substrate at greater than 700° C. toabout 1000° C., the depositing achieving better step coverage thananother step coverage at lower temperatures less than or equal to 300°C.
 26. The method of claim 25 further comprising: forming openings inthe substrate; and depositing the silicon dioxide within the openings.27. The method of claim 25 wherein the gases comprise SiH₄ and oxygen.28. The method of claim 25 wherein the gases comprise SiH₄, oxygen andargon.
 29. The method of claim 11 wherein the substrate temperature isfrom greater than 700° C. to about 1000° C. during at least part of thedepositing.
 30. The method of claim 1 wherein the depositing exhibits adeposition rate to etch rate ratio of at least about 4:1 throughout thedepositing until completing formation of the silicon dioxide layer. 31.The method of claim 12 wherein the substrate temperature is from greaterthan 700° C. to about 1000° C. during at least part of the depositing.32. The method of claim 7 wherein the depositing and etching exhibit adeposition rate to etch rate ratio of at least about 4:1 throughout thedepositing and etching until completing formation of the silicon dioxidelayer.
 33. The method of claim 1 further comprising, while depositingthe silicon dioxide at a deposition rate, etching the deposited silicondioxide with the plasma at an etch rate, a ratio of the deposition rateto the etch rate being at least about 6:1 throughout the etching anddepositing until completing formation of the silicon dioxide layer. 34.The method of claim 1 further comprising, while depositing the silicondioxide at a deposition rate, etching the deposited silicon dioxide withthe plasma at an etch rate to achieve a ratio of deposition rate to etchrate that is at least two-times greater than another etch rate underidentical processing conditions of an identical substrate except atlower temperature conditions less than or equal to 300° C.
 35. Themethod of claim 5 further comprising maintaining a temperature of thesubstrate at greater than 700° C. to about 1000° C. during thedepositing.
 36. The method of claim 5 further comprising, whiledepositing the silicon dioxide at a deposition rate, etching thedeposited silicon dioxide with the plasma at an etch rate, a ratio ofthe deposition rate to the etch rate being at least about 6:1 throughoutthe etching and depositing until completing formation of the silicondioxide layer.
 37. The method of claim 5 further comprising, whiledepositing the silicon dioxide at a deposition rate, etching thedeposited silicon dioxide with the plasma at an etch rate to achieve aratio of deposition rate to etch rate that is at least two-times greaterthan another etch rate under identical processing conditions of anidentical substrate except at lower temperature conditions less than orequal to 300° C.
 38. The method of claim 1 further comprising, whiledepositing the silicon dioxide, etching the deposited silicon dioxidewith the plasma.
 39. The method of claim 25 further comprising, whiledepositing the silicon dioxide, etching the deposited silicon dioxidewith the plasma.
 40. The method of claim 1 wherein the depositingachieves better step coverage than another step coverage at lowertemperatures less than or equal to 300° C.
 41. The method of claim 7wherein the etching and depositing achieves better step coverage thananother step coverage at lower temperatures less than or equal to 300°C.
 42. The method of claim 13 wherein the ratio is at least two-timesgreater than another ratio under identical processing conditions of anidentical substrate except at lower temperature conditions less than orequal to 300° C.
 43. The method of claim 16 wherein the ratio is atleast two-times greater than another ratio under identical processingconditions of an identical substrate except at lower temperatureconditions less than or equal to 300° C.